THURSDAY, May 14 (HealthDay News) -- In a phase 3 clinical trial, an experimental immune-based treatment boosted by 20% the overall survival of those with tough-to-treat neuroblastoma, which affects mostly children.

The findings are to be presented at the American Society for Clinical Oncology annual meeting, which starts later this month in Florida.

The trial involved 226 patients newly diagnosed with high-risk neuroblastoma, a cancer of the nervous system. Standard treatment includes surgery, aggressive chemotherapy with "stem cell rescue" (where the patient's stem cells are removed before treatment, then returned after chemotherapy to boost blood/immune function) and radiation therapy.

"Even though we treat it with aggressive therapy, high-risk neuroblastoma often returns, and most patients do not survive," Dr. Alice Yu, a professor of hematology/oncology at the University of California, San Diego, and the school's Moores Cancer Center, said in a news release from the society.

The new immune-based treatment -- called chimeric anti-GD2 antibody ch14.18 -- targets a key sugar-and-fat molecule lying on neuroblastoma cells called GD2. Left alone, the molecule inhibits the immune system from attacking the cancer cells. But the new antibody binds to GD2, encouraging such attacks, the researchers explained.

In the new trial, half of the patients received chemotherapy/stem cell rescue plus standard treatment (retinoic acid), as well as the new immunotherapy. The others received standard treatment only.

After two years, the number of participants who had survived without a relapse reached 66% in the immunotherapy groups, compared with 46% among those who did not get the new treatment. Overall survival after two years reached 86% in the immunotherapy cohort and 75% among those who got standard treatment.

"It is very exciting to have a new treatment option for this disease," Yu said, "and we hope to make this immunotherapy available to more children with neuroblastoma."

The study is to be presented June 2 at the meeting but was described in a news conference Thursday.